Overpolymers, prepared by first polymerizing a monomer(s) to a given degree of polymerization and/or particle size, then polymerizing other monomer(s) are known to the art. The polymerization steps can be carried further to yield third and even fourth layers or more. The overpolymer can have hard cores (i.e., high glass transition temperature cores having a Tg value of about 20.degree. C. or higher) or soft cores (i.e., cores having a glass transition temperature of about 0.degree. C. or lower). The glass transition temperatures of the various layers can alternate with respect to the core such that an overpolymer will be comprised of, for example, a hard core, soft shell, and hard overcoat. Relevant U.S. Pat. Nos. disclosing and teaching the preparation of overpolymers are 3,657,152; 3,661,994; 3,793,402; 3,803,264 and 4,082,895.
Patents directed to the use of overpolymers in thermoset and thermoplastic molding compounds are U.S. Pat. Nos. 3,632,679; 3,655,826; 3,661,994; 3,760,035; 3,793,402; and 3,652,722; 3,787,522; 3,833,632; 3,833,683; 3,880,950; 3,887,645; and 3,894,115.
In U.S. Pat. No. 4,082,895 there are disclosed overpolymers comprised of a hard predominantly acrylonitrile monomer core, a rubbery shell, and a hard overcoat. These overpolymers have particular utility as tougheners for thermosetting molding compounds such as phenolic resins, furans, epoxy resins, and unsaturated polyester resins, and for thermoplastic molding compounds such as polyvinyl chloride, polycarbonates, polystyrene, polymethacrylates, and polypropylene. Disadvantageously, however, overpolymers containing hard cores tend to be undesirable for uses as high impact high rubber content molding resins due to undesirably low flow properties.
In U.S. Pat. No. 3,944,631, an acrylate rubber based overpolymer comprising a crosslinked alkyl acrylate core polymer, a crosslinked styrene/acrylonitrile shell (optionally the core and shell polymers may be reversed), and a non-crosslinked substantially non-grafted styrene/acrylonitrile overcoat was disclosed.
While previously known acrylate rubbers, including overpolymer rubbers, have achieved a degree of success as impact modifiers for injection molding resins, it is still desirable to provide such a resin having even better toughness and gloss properties. Such a resin may be achieved by the use of overpolymer rubbers having improved properties.